My one year old a/c cools in morning, when it gets hot outside it can.t keep up and runs allday but it worked last year just fine it ran for 15 min. off for 20 about... nothing in the house has changed insulation .doors .windows. a/c man came by said nothing wrong with it,freon good elictical good fan good... but in hard start .new capasitor. So far . If u need more ask I'll email back... thanks

Is your filter clean? Are the coils outside clean and free of grass clippings leaves etc? What is the temperature and the vent? What is the temp at the return?

You might want to look at the cleanliness of the evaporator coil, if this gets dirty it will restrict air flow there by reducing the efficient operation of the system.